Schafer U.S. Pat. Nos. 3,193,437 and 3,193,441 illustrate the concept of an initially resilient and open-cell foam material impregnated with a thermosetting resin used alone or in combination with reinforcing fibers, and wherein the foam layer is compressed under relatively low pressures such that the resin substantially fills the cells of the foam and which resin is cured while maintaining the resilient foam layer in a compressed condition. While in both Schafer patents it is stated that a polyester resin is preferred, it is also recognized that as an alternative epoxy or other resins may be used. Likewise, U.S. Pat. No. 3,867,221 Chant teaches that polyester or epoxy resins may be used as the binder in a foam-impregnated composite structure. U.S. Pat. No. 3,269,887 Windecker also teaches the alternative use of polyester or epoxy resins in fabricating a resin-impregnated foam composite.
Thus, the prior art has heretofore taught that in forming a resin-impregnated foam composite one must use a single resin binder system, e.g. either polyester or epoxy. There is no recognition in the prior art that at least two resin binder systems can be combined to yield a resultant composite structure having the desirable physical and chemical characteristics of each cured resin.